1. Field of the Invention
The present invention is broadly concerned with new siloxane bodies having unique nanoscale morphologies. More particularly, it is concerned with such siloxanes, which may be in the form of elongated wires, tubes, filaments or coils, as well as methods of synthesis thereof using nanoparticle metal catalysts.
2. Description of the Prior Art
Siloxanes are polymeric compounds having repeating O—Si—O moieties or monomers which form a backbone, with a variety of substituents (e.g., alkyl groups) bonded to the Si atoms. A classic example of siloxanes are the polyorganicsiloxanes used as synthetic rubbers. These products have many advantages including thermal stability, the ability to repel water and form tight seals. They also have excellent resistence to oxygen, ozone and sunlight degradation, and exhibit good electrical insulative properties, low chemical reactivity and low toxicity.
Small and nanoscale metallic particles have been used as catalysts in the past. The small size of the metallic particles, apart from increasing the surface area, also renders the particles more active catalytically by exposing active sites on the metal surface to incoming reagents. Noble metals such as gold which are not active in their bulk state, can be good catalysts when their size is decreased to the nanometer level. Gold particles have been used as oxidation catalysts for toxic fumes such as CO and NO. Additionally, metallic nanoparticles such as gold, cobalt and iron have been shown to be good catalysts for preparing carbon and silicon nanotubes and other nanostructures.
However, prior use of metallic nanoparticles as catalysts has required rather high temperatures. For example, one high temperature process for the production of nanowires involves promotion of anisotropic crystal growth using metal particles as catalysts. This involves a vapor-liquid-solid (VLS) mechanism involving metal alloying, crystal nucleation and axial growth. This process requires very high reaction temperatures, and yields nanowires only of limited length.
Gold nanoparticles are known to be stabilized by a variety of ligands. It has been previously reported that nearly monodisperse gold nanoparticles can be prepared by carrying out a digestive ripening (refluxing a polydisperse colloid suspended in a solvent with a suitable capping agent) protocol with different ligands such as alkanethiols, phosphines, amines and silanes. Among these ligands it was clearly established by Banaszak Holl and coworkers that when silanes are attached to gold surfaces they lose hydrogen resulting in weak Au—Si covalent bonds. It has also been demonstrated that large amounts of gold and other metal colloids can be prepared in polar solvents such as acetone, butanone and pentanone. TEM pictures of the as-prepared colloids reveal that the gold nanoparticles are highly polydisperse and also highly defective in nature.